2013-12-14 13:47
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Consider this program:

package main

import "fmt"
import "time"
import "runtime"

func main() {

    x := 0

    go func() {
        time.Sleep(500 * time.Millisecond)
        x = 1

    for x == 0 {

    fmt.Println("it works!")

Why does it terminate locally but not on Playground? Does the termination of my program rely on undefined behavior?

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  package main 
import  “ fmt” 
import“ time” 
import“ runtime” 
func main(){
x:= 0 
 go func(){
 time.Sleep(500 * time.Millisecond)\  nx = 1 
 x == 0 {
 fmt.Println(“ it works!”)

为什么它在本地终止,而不在游乐场终止 ? 程序的终止是否依赖未定义的行为?

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3条回答 默认 最新

  • duankan8739 2013-12-14 20:54

    That code doesn't offer much guarantees. It's relying almost entirely on implementation details around undefined behavior.

    In most multi-threaded systems, there's no guarantee that a change in one thread with no barrier will be seen in another. You've got a goroutine which could be running on another processor altogether writing a value to a variable nobody's ever guaranteed to read.

    The for x == 0 { could quite easily be rewritten to for { since there's never a guarantee any changes to that variable might be visible.

    The race detector will also probably report this issue. You should really not expect this to work. If you want a sync.WaitGroup you should just use one as it properly coordinates across threads.

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